|Publication number||US20080239299 A1|
|Application number||US 12/137,007|
|Publication date||Oct 2, 2008|
|Filing date||Jun 11, 2008|
|Priority date||Dec 4, 2006|
|Also published as||US7649189|
|Publication number||12137007, 137007, US 2008/0239299 A1, US 2008/239299 A1, US 20080239299 A1, US 20080239299A1, US 2008239299 A1, US 2008239299A1, US-A1-20080239299, US-A1-2008239299, US2008/0239299A1, US2008/239299A1, US20080239299 A1, US20080239299A1, US2008239299 A1, US2008239299A1|
|Inventors||Barrett E. Cole|
|Original Assignee||Honeywell International Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (7), Classifications (11), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a continuation-in-part of U.S. patent application Ser. No. 11/770,648, filed Jun. 28, 2007, which is a continuation-in-part of U.S. patent application Ser. No. 11/633,872, filed Dec. 4, 2006.
U.S. patent application Ser. No. 11/770,648, filed Jun. 28, 2007; U.S. patent application Ser. No. 11/633,872, filed Dec. 4, 2006; and patent application Ser. No. 10/953,174, filed Sep. 28, 2004, now U.S. Pat. No. 7,145,165, are hereby incorporated by reference.
The present invention pertains to sensors and particularly to cavity ring down sensors. More particularly, the invention pertains to the structure of the sensors.
The invention is a cavity ring down sensor having a fiber optic element coupled at a normal to a surface of the input mirror of the cavity of the sensor.
The present invention may permit a fiber optic element to be easily mounted to a mirror so that light can be injected into the CRDS cavity from an external laser. This appears particularly important for the case of a CRDS system mounted in, for instance, a two inch well head with little room for the fiber to bend. Also the invention may provide an ability to fine tune the system so that the light from the fiber can be optimized in the cavity.
Two substrates of different materials may be mounted against each other with their common face at an angle relative to the normal to the mounting axis. The angle between the two substrates may be defined by the indices of the materials and be chosen so that light normal to the mounting axis and delivered along this axis by the fiber element is refracted into the cavity at an angle that is one of the beam leg directions. This approach may couple the light into the cavity efficiently.
The inner element (for instance, having SiO2) may be optically sealed to the block. The second element (for instance, having Si) may be allowed to translate across the surface of the SiO2 substrate thus providing fine tuning for the position of the fiber which is mounted to the backside of the Si substrate. For optimal performance, the external surfaces should be coated with an antireflection coating.
The mirror may be attached to the CRDS cavity so that light is made to enter the cavity. The position of the wedge to which the fiber is attached may be fine tuned for a maximum fluence into the CRDS cavity. Once achieved, the whole device can be potted to lock in the fine tuned position if desired.
For ground water measurements, the block may be lowered into a well, the block being in a liquid water tight chamber. Vapors from the water may be transmitted through a membrane into the cavity where they are absorbed if the proper wavelength is put into the cavity. The use of this wedge mirror assembly may permit the fiber input to be normal to the CRDS cavity. This mirror should be transmissive and so the inner element made of SiO2 may be either a curve or a flat as opposed to one with a transducer mounted on it for tunability. This system may work for wavelengths where both Si and SiO2 transmit the input radiation. An SWIR band between 1.5 and 2.0 microns may be one of the wavelength ranges of input radiation where the gases have significant absorption.
As shown in
There may be fast trace gas impurity measurements of critical molecules such as trichloroethylene (TCE), dichloroethylene (DCE), H2O, CO, NH3, HF, HCl, CH4 and C2H2. Such measurements may be made in seconds. Trace moisture concentration may be measured at levels from parts per billion (ppb) to parts per trillion (ppt).
Tunnel laser 61 may send a continuous wave (or possibly pulsed) light signal to cell 62. Signal 64 may be regarded as a signal 66 that is reflected around in cell 62 from mirror 71, to mirror 72, to mirror 73, to mirror 71 and so on until the signal 66 diminishes. Some light 65 may leave cell 62 and impinge detector 67. Detector 67 may convert light signal 65 to an electrical signal 68 that goes to a data acquisition and analysis unit 69. Control electronics 74 may send control signals 75, 76 and 77 to tunable laser 61, detector 65 and data acquisition and analysis unit 69, respectively. Also, a control signal 90 may be sent to a moveable support 79 of mirror 72 to provide tenability of the path for light 66. Support 79 may be a piezoelectric transducer to allow tuning and modulation of the path length of cell 62.
One may detect a certain fluid using a laser tuned on a transition band, near a particular frequency. A fluid may be a gas or liquid. Using system 62, one may be able to measure the concentration of the fluid in some medium. The certain fluid and associated medium may enter a port 78 and exit a port 79. Port 81 may be for a connection to a pump. Port 82 may be used for a gauge. One or more hollow optical fibers to and from the ring cavity may be used provide gas to take gas from the ring cavity. The gas may be compartmentalized in the cavity with Brewster windows.
The system 60 may provide for an intrinsic measure of absorption. The CRDS sensitivity may equal
Another relationship may be:
Typical sensitivity may be at about 10−6 to 10−10 cm−1 for multimode light and about 10−9 to 10−12 cm−1 for single mode light.
The system 62 may be built on the strengths of a MEMS etalon, various laser system technologies and VCSELs. A laser gyroscope cavity may be used as a ring-down cavity.
At the corners of cavity 711, there may be mirrors 716, 717 and 718. Mirror 716 may partially reflect light 713 in the cavity so that detector 715 may detect some light in the cavity for analysis purposes. On mirror 716 may have a small hole for input and output for light 713. In this case, the mirror 716 may be fully reflective. Detection of light 713 may note intensity versus time, frequency, and other parameters as desired. The output of the detector or monitor 715 may go to a data acquisition and analysis circuit 719 for such things as acquisition, analysis and other purposes for obtaining information about a sample fluid in the cavity 711. One purpose may be for tuning the laser 712 to an adsorption line of the sample. The detector output to the readout and control electronics 721 may be improved with a dual JFET amplifier. Other circuits may be utilized for detector output processing. Readout and control electronics 721 may provide an excitation and control for light source 712. Inputs and outputs may be provided to and from a processor 722 relative to connections between the processor 722 and readout and control electronics 721 and data acquisition and analysis circuit 719. Processor 722 may also be connected to the outside 723 signals going in and out of system 710. A user interface may be effected with the readout and control electronics 721 and/or the outside 723. Readout and control electronics 721, data acquisition and analysis circuit 719, and processor 722 may constitute an electronics module 724. Electronics module 724 may have other components. Ports 725 may provide for input and output of a sample fluid to and from the cavity 711.
A mirror mounting device 310 and approach for beam path alignment of a system 312 are illustrated generally in
As seen in
As seen in
Trace gas detection and identification with very high sensitivity may be achieved using cavity-ring-down technique implemented with ring-laser gyro fabrication and alignment technology in order to achieve cost-effective producibility.
The advantages of adapting ring laser gyro fabrication methods (laser block, mirror fab, attachment, and alignment, and so forth) may achieve a cost-effective system for cavity-ring-down gas detection. The present system has an approach for coupling light into and out of the ring cavity. In particular, the approach provides for directing light incident from the source normally onto the optical input port of the ring cavity in order to facilitate alignment of the source to cavity, and then interposing a prism coupling module to direct the light into the ring cavity. A variation of this approach includes a modification of the coupling prism introduced before the optical input port so as to also couple light in the cavity to an external detector, thus allowing the same cavity port to be both an input and output port without return light being fed back into the source.
A light conveyance mechanism or channel or an optical fiber 101 may convey light into cavity 103 via the interface 104 and mirror 107. If situated appropriately on surface 113, light conveyance mechanism 101 may convey light out of cavity 103 via mirror 107 and interface 104. Or light may exit the cavity to a light detector 114 with an electrical signal indicating a light signal on a conductor 116. For an illustrative example, optical fiber may be situated with an end optically in contact with portion 109 via surface 113. The core of the fiber 101 conveying the line may be parallel to a normal of surface 113 or perpendicular to surface 113. Also, a light beam 115 may be perpendicular to surface 113 as it enters portion 109 and go straight to portion interface 111. At interface 111, light beam 115 may deviate from the straight path and head in another direction due to a different index of refraction of portion 105 relative to the index of portion 109. The path of light 115 may be calculated with Snell's law, n1 sin θ1=n2 sin θ2. Light 115 may again be refracted as it enters cavity 103. The index of refraction may be regarded as the same as air. The path of light 115 may be determined with certain dimensions of portions 105 and 109, among other parameters and factors, including the indices of refraction of the materials traversed by light 115. The surfaces 113 and 112 and mirror 107 may be designed to be parallel; however, other approaches may be implemented.
Examples of materials for portions 105 and 109 may include fused silica and silicon, respectively. The silica may have an index n of about 1.46. Silicon may have an index n of about 3.6.
Light 115 may go in a clockwise direction along the optical path 114 which makes direction changes at two corners 108 due to mirrors 110, respectively, and corner 102 due to mirror 107. Since mirror 107 may be semitransparent, some light 115 may go through mirror 107, portion 105, interface 111 and portion 109 to detector 114 for amplitude measurement. The amount of amplitude of the returning light 115 at detector 114 may be indicative of a certain gas in the cavity, particularly such as after the light entering cavity from conveyance or fiber 101 ceases. A decrease of the amplitude of light 115 may be regarded as a ring-down or decay of the light 115 in the ring-like path 114 of cavity 103. Conveyance mechanism or fiber 101 may be attached to and/or secured into its perpendicular position relative to surface 113 with a fastener, epoxy 117, or the like.
In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense.
Although the invention has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US7864326||Oct 30, 2008||Jan 4, 2011||Honeywell International Inc.||Compact gas sensor using high reflectance terahertz mirror and related system and method|
|US7884938||Jan 29, 2009||Feb 8, 2011||Honeywell International Inc.||Multiple beam wide band CRDS cavity sensor and detector|
|US8198590||Oct 30, 2008||Jun 12, 2012||Honeywell International Inc.||High reflectance terahertz mirror and related method|
|US8528429 *||Jan 20, 2010||Sep 10, 2013||Babcock & Wilcox Power Generation Group, Inc.||System and method for stabilizing a sensor|
|US20110168876 *||Jul 14, 2011||Hsiung Hsiao||Optical module and system for liquid sample|
|US20110174053 *||Jul 21, 2011||General Electric Company||System and method for stabilizing a sensor|
|EP2166323A1 *||Sep 15, 2009||Mar 24, 2010||Honeywell International Inc.||Cavity ring down system having a common input/output port|
|Cooperative Classification||G01N21/8507, G01N2021/0378, G01N21/39, G01N2021/855, G01N21/031, G01N2021/0385|
|European Classification||G01N21/03B, G01N21/85B, G01N21/39|
|Jun 11, 2008||AS||Assignment|
Owner name: HONEYWELL INTERNATIONAL INC., NEW JERSEY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:COLE, BARRETT E.;REEL/FRAME:021079/0748
Effective date: 20080609
|Mar 18, 2013||FPAY||Fee payment|
Year of fee payment: 4